1. Field of the Invention
This invention relates to gas laser oscillators. More specifically, it relates to high-speed axial flow type gas laser oscillators in which the laser gas flows in the direction of the laser beam.
2. Description of the Prior Art
In a gas laser oscillator, the laser amplification effect occurs inside a laser tube where a plasma is produced. It is known that increasing the length of a laser tube results in an increase in output because it increases the volume occupied by plasma. Consequently, to increase the laser output, the laser tubes of a gas laser oscillator should be increased in length. However, increasing the length of the laser tubes poses problems both technologically and in terms of the amount of space required. Therefore, in general, a plurality of laser tubes are arranged parallel to each other and reflecting mirrors are placed at the connections between tubes, thus increasing the effective overall length. In addition, it is known that in a gas laser oscillator, by cooling the laser gas the population inversion is accelerated and the laser oscillation efficiency is increased. Consequently, in general the laser tubes are cooled, or else the laser gas is cooled in a heat exchanger and then injected into the laser tubes at high speed: The laser gas heated by the electric discharge is immediately recirculated back to the heat exchanger where it is cooled again. In addition, to improve efficiency in a gas laser oscillator it is also necessary to improve the efficiency of use of the electric power used for injection.
Conventional high-speed axial flow type gas laser oscillators have a cooler or heat exchanger to cool the laser gas in the laser tubes and a blower to inject the gas into the tubes at high speed, and then the gas is recirculated from the laser tubes to the heat exchanger. However, the lengths of the recirculation paths from the laser tubes to the heat exchanger or cooler are not constant in the prior art gas laser oscillators. This means that the resistances to gas flow in the different recirculation paths are not equal, which produces inequalities in the flow rates and thus in the temperature of the laser gas within the different laser tubes.
That is to say, in the tubes which receive laser gas which has circulated at lower flow rates than the laser gas entering other laser tubes, the temperature is higher, meaning that the population inversion is reduced and, in turn, the laser output is reduced, and this in turn affects the mode of the laser beam. Consequently, the different flow rates of the laser gas entering different laser tubes is a cause of lower output and fluctuations in output from the entire gas laser oscillator.
In addition, the gas which is recirculated to the heat exchanger from the laser tubes in a gas laser oscillator is a kind of plasma because the gas has been ionized by electrical discharges inside the laser tubes. This in turn means that the gas becomes electrically conducting, so that wasteful electrical discharges, which do not contribute anything to the pumping of the laser gas, occur between the heat exchanger and the cathodes of the laser tubes, producing a large loss of electrical power used for injection. In addition, these electrical discharges heat the laser gas further, imposing an additional load on the heat exchanger or cooler.
Also, in the prior art gas laser oscillators, there is a troublesome problem in removing and replacing electrodes. For stability of the electrical discharges and good condition of the flow of the laser gas inside the laser tubes, it is required that the electrodes be ring-shaped. Also, to reduce the contact resistance between the electrodes and the electrode holders, the electrodes are shrink fitted to the electrode holders which are coupled to the laser tubes. Consequently, since each electrode holder must be removed from the laser tube in order to replace the electrode, the problem that the laser tube must be displaced in the axial direction arises.
In addition, in the prior art gas laser oscillators, since the support plates which support the laser tubes are fixed to the base, there is the problem that it is difficult to compensate for the heat deformation of the support plates and surrounding parts.